This invention relates to gas lasers, and more particularly to an atomic fluorine laser operating in the vacuum ultraviolet region.
Many gases, both molecular and atomic, can absorb energy which raises their electrons to an excited state. The excited state has a tendency to return to the lowest or ground state. When an electron in an excited state returns to a lower or ground state, energy in the form of electromagnetic radiation is given up. This radiation has a wavelength corresponding to the difference between the two energy levels involved. The wavelength of the electromagnetic radiation emitted is described by the relationship ##EQU1## where .lambda. is the wavelength of the emitted radiation, h is Planck's constant, c is the speed of light, and .DELTA. E is the difference in energy between the upper and lower energy levels. Not all wavelengths emitted for a given gas can be used for a laser. Only those excited states where population inversion occurs result in lasing action.
The arc spectrum of atomic fluorine has been investigated for many years. While many lines and energy levels have been identified for atomic fluorine, this is not sufficient to determine which, if any, transitions between energy levels result in lasing action.
Certain transitions in atomic fluorine have been demonstrated to be useful lasers in the visible region of the spectrum. U.S. Pat. No. 3,676,797 to Kovacs describes an atomic fluorine laser producing a visible beam of laser energy at 7039 .ANG., 7129 .ANG., and 7204 .ANG.. Kovacs uses a mixture of a fluorine containing gas and helium in a resonant optical cavity. A pulsed electric discharge across the gas mixture dissociates the fluorine-containing gas and generates sufficient fluorine atoms in an excited state to produce a population inversion. A visible output at 7039 .ANG. to 7204 .ANG. is obtained by adjusting the mirrors of the optical resonant cavity.
U.S. Pat. No. 3,882,414 to Jeffers et al. also describes an atomic fluorine laser producing a visible beam of energy at 7037.45 .ANG., 7127.88 .ANG., and 7800.22 .ANG.. The Jeffers laser differs from the Kovacs laser in the manner in which the fluorine atoms are excited. The Jeffers laser is a dissociative transfer laser. The gaseous mixture consists of helium, hydrogen fluoride, and molecular hydrogen. An electric discharge excites the helium atoms into a metastable state; collisions with the hydrogen fluoride molecules then result in the formation of atomic fluorine in an excited state to produce a population inversion. The Jeffers laser is also operated as an oscillator, using an optical resonator cavity.
More recently, Sadighi-Bonabi et al., J. App. Phys. 53(5), May 1982, described laser output in an atomic fluorine laser at 745 and 635 nm (7450 .ANG. and 6350 .ANG.), both of which are in the visible range. Sadighi-Bonabi et al. achieve their lasing effect by ion-ion recombination of He.sup.+ and F.sup.-.
The foregoing atomic fluorine lasers are to be distinguished from the well known excimer lasers. In an excimer laser, such as the one described in U.S. Pat. No. 4,177,435 to Brown, the lasing medium consists of a rare gas and a halide. The rare gas and halide form a temporary molecule, such as ArF, which is excited to create a population inversion, which produces a laser output at wavelengths completely different from those of the individual constituent gases.
While lasers operating in the visible range are useful, they have less energy than those operating in the ultraviolet and vacuum ultraviolet regions. From equation (1) it can be seen that as .DELTA. E increases, .lambda. decreases. A laser operating in the vacuum ultraviolet region has a significantly greater energy than one operating in the visible or infrared region.
Therefore, it is an object of the present invention to provide an atomic fluorine laser operating in the vacuum ultraviolet region of the spectrum.
It is also an object of the present invention to provide an atomic fluorine laser operating at heretofore unknown wavelengths.
The foregoing and other objects, features, and advantages of the present invention will become more apparent in light of the following description and accompanying drawings.